As fossil fuels including gasoline, diesel oil, kerosene, LNG, LPG, etc. become exhausted, the prices of fossil fuels rise rapidly, and thus there is an urgent need for the development of technologies capable of increasing the combustion efficiency of the fuels. In addition, as environmental standards become more stringent, there is a need for the development of various devices capable of reducing toxic gases that are generated during combustion of fossil fuels. Such technologies include temperature sensors that are installed in vehicle exhaust devices. In particular, in the case of diesel vehicles, regulations for dust, NOx and the like, which are generated during combustion, have become more stringent, and thus it is almost essential to mount exhaust devices that can reburn toxic gas or convert toxic gases into non-toxic gases. A temperature sensor that is used in the exhaust device should basically exhibit optimal efficiency even at a temperature equal to or higher than 500° C., and thus is required to have high precision and strong durability. In addition, since there is a great difference in temperature between the daytime and nighttime, seasons, and areas in which vehicles are driven, it should be possible to measure temperature over the temperature range of about 0° C. to 900° C.
In general, temperature sensors are manufactured using metals or metal oxides. In particular, temperature sensors that are used in high-temperature environments are made mainly of metal oxides. For the manufacture of temperature sensors made of metal oxides, transition metal oxides, such as Fe2O3, NiO, Cr2O3, MnO2 or the like, are mainly used. Generally, the transition metal oxides are mixed with sintering aids or resistance regulators, such as Al2O3, SiO2, Y2O3 or the like, and subjected to ceramic processes including calcination and sintering, after which they are manufactured into temperature sensors. Generally, such ceramic temperature sensors exhibit a very high resistance of 106 ohm or higher at room temperature, and exhibit a resistance of a few ohms at high temperature equal to or higher than 700° C. Thus, it is not easy to increase the high-temperature resistance of most ceramics.
As described above, a temperature sensor to be used in a vehicle exhaust device should be measured with a universal meter over a wide temperature range from a low temperature of about 0° C. to a high temperature of about 900° C. To satisfy this condition, the resistance of the metal oxide that is used in the temperature sensor should be about 1 Mohm at 0° C., and about 30 ohm or higher at 900° C. Accordingly, the general ceramic temperature sensors as described above were not suitable for use in vehicle exhaust devices. In addition, metal oxide temperature sensors according to the prior art were manufactured according to the classification, depending on the environment in which they would be used, into a temperature sensor for low-temperature use, a temperature sensor for intermediate-temperature use, and a temperature sensor for high-temperature use. Meanwhile, ZrO2 has been used mainly as a temperature sensor for high-temperature use of equal to or higher than 500° C. because it has an infinite resistance value at room temperature.
Accordingly, in order to solve the problem in which the high temperature resistance of conventional ceramic temperature sensors is significantly lowered, the present inventor has completed the present disclosure intended to provide a technology for manufacturing a temperature sensor that is manufactured by heat-treating either an insulating material having high-temperature stability or a high-resistance ceramic material at a high temperature to prepare a high-resistance material having a large particle size, and mixing the high-resistance material with a low-resistance material having a small particle size to increase the total resistance, and that can precisely measure temperature over the temperature range from 0° C. or lower to 900° C.